1. Field of the Invention
The present invention relates to a device for controlling an exposure for an imaging device provided in a digital camera, and more particularly to a device for controlling a dark exposure in order to detect a noise component of an image signal caused by a dark current generated by the imaging device.
2. Description of the Related Art
A dark current is generated in an imaging device when the imaging device does not receive light. The longer the exposure time, the greater the influence on the photographed image. Conventionally, there is known a device in which a dark exposure is carried out every time a main exposure is performed, and image data obtained by the dark exposure is subtracted from image data obtained by the main exposure to reduce the influence of the dark current, as disclosed in U.S. Pat. No. 5,729,288.
In the dark exposure, the blockage of light may be insufficient when closing only the shutter. For example, when a car passes a place where astronomical photography is being carried out, if strong light from the headlights enters the camera body through the photographing lens, the light may leak into a light-receiving surface of the imaging device through the closed shutter. In a conventional single-reflex camera, a dark exposure is carried out while the mirror is moved down, and part of the light passing through the photographing lens is blocked by the mirror. Therefore, an amount of light entering the imaging device is relatively small. Conversely, in a mirrorless-type camera, which is a recent development, light passing through the photographing lens strikes the shutter directly, and thus the light may easily enter the imaging device.